1. Technical Field
The present invention relates in general to improved H configuration drive circuits and in particular to an improved H configuration drive circuit which includes fault detection and protection circuitry. Still more particularly, the present invention relates to a magnetic tape recorder write head drive circuit which provides integral component fault detection signals which may be utilized to identify component failures.
2. Description of the Related Art
H configuration drive circuits are well known in the prior art. Such circuits are typically utilized in applications in which current is to be supplied in one of two directions to a load, such as a magnetic write recording head. In such circuits, power dissipation is a significant concern. For example, in tape recorder units a need has been recognized for smaller tape products. However, in such small products little or no space is available for cooling fans or similar devices. Pockets of thermal energy or hot spots are then created which may have a deleterious effect on the electronics circuitry within the tape product. Hence, there is an ongoing and recognized effort to reduce the power dissipated by the write driver circuit within small form factor tape units to minimize the amount of heat generated thereby.
An early example of an H configuration driver circuit is disclosed in U.S. Pat. No. 3,037,200, issued to Robert N. Mellott and entitled "Computer Magnetic Drum Writing Circuits." This patent discloses a tandem amplifier system which utilizes four amplifiers to control the energization of a load by the circuit in response to bivalued input signals. A similar H configuration driver circuit is disclosed in "Predriver for `H` Configured Write Driver for Magnetic Recording" by J. A. Bailey, R. G. Black, Jr., and J. Lewkowicz, IBM Technical Disclosure Bulletin, Volume 23, No. 11, November 1981, which discloses a write driver for a thin film magnetic write head. The driver transistors therein are connected in an H configuration with two driver transistors being turned on to produce current through the head in one direction and the other being turned on to provide current through the head in the other direction. In such a circuit the voltage excursions on the two sides of the head are not equal and opposite. Thus, transients may be capacitively coupled to the read circuitry.
More recently, U.S. Pat. No. 4,551,772 issued to David E. Sliger and assigned to Storage Technology Corporation discloses a write drive circuit which utilizes current mirrors to reduce feed-through. Additionally, an H write driver utilizing a plurality of bipolar drive transistors has been disclosed in U.S. patent application Ser. No. 07/991,864, filed Dec. 15, 1992, and assigned to the Assignee herein named. In the aforementioned application, a novel circuit is included for driving the upper bipolar drive transistor wherein the transistor is adapted to sense the output of the drive transistor and regulate a voltage at the input thereof in response thereto in order to keep the drive transistor out of the saturation region.
Thus, those having skill in the art will appreciate that H write driver circuits are relatively fast and have generally low power dissipation. However, an increased desire on the part of consumers of such devices for higher reliability and serviceability has created a need for driver circuits which include integral component fault detection for efficiently detecting component failures within a so-called "Field Replaceable Unit" (FRU) such that service personnel may rapidly and efficiently determine which component has failed, in order to facilitate repair or replacement of that device. It should therefore be apparent that an H write driver circuit having integral component fault detection circuitry would be highly desirable.